The World Health Organization (WHO) defines any noise above 65 decibels as noise pollution. In residential developments, the BS8233:2014 states that the noise in each habitable room should not exceed 35 dB and indicates that restful sleep is possible only if ambient noise levels are below 30 dB. If for example loud traffic noise registers 65-70Db, then the building must be able to reduce the noise level by 35-40Db.
It’s important to understand that external noise in residential projects can impact each housing block differently, so the acoustic assessment should be carried out for each elevation, to make sure that the correct sound reduction strategy is implemented across the whole project.
There can be several dB difference between the three sound reduction figures Rw, Rw+C and Rw+Ctr for the same window.
Rw is the ‘weighted sound reduction index.’ It is a number used to rate the effectiveness of the glass as a noise insulator and is measured in decibels (dB).
The spectrum adaption terms C and Ctr are used to take into account different source spectra.
Ctr for example is an adjustment factor which is used to account for low frequency noise - typically the biggest problem with sound insulation. Ctr is always a negative number, so the Rw+Ctr will always be less than the Rw value. Many sound insulation types will represent how effective they are by displaying the Rw/Rw+Ctr values together.
It is therefore important to clarify whether the requirements for reduction figures are stated in Rw, Rw+C or Rw+Ctr.
In the UK residential market an acoustician is generally appointed to assess the noise level on site and advice on the best strategy to achieve the sound reduction target. Detailed information on requirements and façade noise levels are vital for VELFAC, as these impact on the windows configuration (materials, type of glass and window size) and ultimately on the price.
Specify your project’s sound reduction targets (Rw, Rw+Ctr or Rw+C) in your tender package. The sound-reducing effect of the window depends on the glazing construction and the window size, sash, frame and joint sealing. Therefore, it is important that tests are conducted of the entire window element and not only the glass.
Also be aware that the higher the sound reduction requirements are, the more limitation there will be in terms of windows size and opening functions.
At VELFAC, we can help you achieve your project-specific acoustic requirements. Contact us as early as possible in your design process so we can provide test evidence and advise on the best solution for your project.
"When we advise on a specific project, we take into account all the relevant factors such as sound pressure on the façade, room size, reverberation time and the total window area. All these elements are supported by test documentation, so you can be sure the products you specify match the requirements of your project."
- Neil Edwards, Specification Consultant, VELFAC
Visit our technical product database to learn more about acoustic performance and test results for our VELFAC 200 Energy system.
- David Lomax, Senior Associate at Waugh Thistleton Architects